1. Field of the Invention
The present invention relates to a valve for regulating a fluid flow of the type having a valve housing with an inlet for the fluid to be regulated, an outlet for a regulated flow of fluid, a valve seat with a valve opening arranged in the valve housing and a valve body, movably arranged against the valve seat, for regulating the flow of fluid through the valve opening.
2. Description of the Prior Art
The term "fluid" as used herein refers to both liquids and gases. When the regulation of gas is described, the same description also applies to regulation of liquid, and vice-versa.
A valve is described in U.S. Pat. No. 5,265,594 having a gas inlet which opens onto a valve seat in a valve housing. A membrane and a piston are arranged at the valve seat to interact in regulating the flow of gas through the valve seat. The piston is spring-loaded, causing the membrane to press against the valve seat. A solenoid coil is arranged around the piston. When the solenoid coil is activated, the piston is electromagnetically forced against its spring-loading, and the membrane is pushed away from the valve seat by the gas in the inlet and a flow of gas then streams through the valve opening to an outlet for regulated gas. This known valve displays very good dynamics and is capable of regulating flows ranging from a few ml/s to a number of liters/s, with great accuracy. It also has a very fast response time and can change from regulation of small flows (ml/s) to regulation of large flows (lls) in only a few tenths of a second. The known valve can also regulate a flow of liquid in the corresponding manner.
These properties make this known valve particularly suitable for use in e.g. medical equipment such as ventilators and respirators. As a result of its extensive dynamics, a ventilator equipped with this known valve can be used for the treatment of both premature babies and adults. The rapid response time means that the ventilator is also able to respond very rapidly to spontaneous breathing. A patient under treatment on the ventilator never needs to feel any great resistance to breathing, something which otherwise occurs with valves lacking the same response time. A patient who e.g. takes a deep breath may require a change in flow from zero to a number of liters/s, in an initial phase of inspiration. The known valve is used e.g. in the Servo Ventilator 300, Siemens-Elema AB, Solna, Sweden
Since the known valve has a relatively complex structure, it occupies a relatively large amount of space in a ventilator, is relatively expensive to manufacture and consumes a relatively large amount of energy in operation. For these reasons, this known valve is not particularly suitable for use in e.g. small, portable, battery-powered ventilators. Thus there is a need for a smaller, less energy-consuming valve whose performance is at least on a par with that of the known valve. Such a valve, preferably, should also be simpler and, accordingly, less expensive to manufacture without sacrificing valve reliability.